The invention relates to an apparatus for coating substrates with a coating material using the EB/PVD method having a crucible arrangement comprised of at least two crucibles disposed offset from one another in a horizontal plane, which crucible arrangement is disposed in a frame that can be displaced horizontally, wherein at least one shaft for accommodating a material bar comprised of the coating material is disposed in the frame beneath each crucible, and having at least one lifting device, by means of which a material bar disposed in the shaft can be inserted through the base of the crucible into crucible, in order to be vaporized there by bombardment with an electron beam from an electron gun.
This type of arrangement is known. Two pairs of crucibles are disposed symmetrically on the head of a rotating base so that, by rotating the rotating base 180°, the crucibles of the one pair change places crosswise with the crucibles of the other pair. A carousel having several shafts, in which material bars are stockpiled, is situated beneath every crucible. Every material bar is made up of several short solid cylindrical segments. Once a material bar has been used up except for the last segment, said segment will get stuck in the crucible so that the carousel under the crucible is able to continue to rotate unhindered until a filled carousel shaft is again located under the crucible carousel. The lifting device pushes the new material bar against the segment remaining in the crucible, thereby releasing it from being stuck. Because the pushed-in material must correspond to the material of the remaining segment, a carousel is loaded with material bars made of one material.
The lifting device in the known apparatus is made of spindle drives, which are fastened on the wall of the vacuum chamber in which the apparatus is disposed.
Arranging a total of four crucibles with the associated carousels on a frame creates an arrangement, which, particularly in the case of a large load of material, is only able to be rotatably mounted on a vertical axis in a large installation space. The lifting devices disposed externally around the frame increase the installation space even more so that it is necessary to provide a large vacuum chamber.
The object of the invention is creating a compact system, which also operates in a trouble-free manner even when heavily loaded with material.
Therefore, to solve the problem, the invention provides that each crucible is assigned a lifting device, which is disposed in the frame, and that the frame can be displaced linearly in the direction of the offset of the crucible.
The advantage of the apparatus according to the invention is that a linear guidance with the same precision requires less installation space than a rotating arrangement so that it is also possible to dispose the lifting devices on the frame. They are thereby in a fixed spatial relationship with the carousels so that a precise interaction of the lifting device with the respectively associated carousel is ensured.
The carousels may now be filled with different materials for different substrate layers. The individual layers are applied successively, in that the frame is displaced linearly so that the respective crucible with the material that is currently to be vaporized is located in an operating position, where it can be reached by an electron beam. The location of the operating position is limited because large parts of the upper side of the frame with the crucible are located in the shadow of the substrates and their holders.
The problem of the shadow occurs because the electron gun is able to be disposed only above a coating zone, which lies above the crucibles and in which the to-be-coated substrates are situated. Because the substrates and their holders fill up the coating zone to a large extent, only a restricted space remains for guiding the electron beam to the crucibles. A substrate receptacle is made, for example, of two elongated, horizontally running holders, on which several substrates are held next to one another. Therefore, the electron beam is only able to move in a vertical plane, which lies between the two holders. Areas to the side of this plane are in the shadow of the substrate receptacles. For this reason, the individual crucibles must be pushed into the vertical plane to arrive at their operating position so that they can be reached by the electron beam.
If the frame is moved linearly from one end position into the other end position by a distance corresponding to the offset of the crucibles of a crucible arrangement, then the one crucible assumes the operating position of the other crucible so that said crucible can now be reached by the beam of the electron gun.
The crucible arrangement is preferably one of two crucible arrangements, wherein the crucibles of both crucible arrangements have the same offset so that in the operating position, material from each of the two crucibles is able to be vaporized.
In order to make sufficient material available without the vacuum chamber needing to be opened, each crucible is assigned a carousel having several shafts, wherein each carousel is rotatably mounted around a vertical axis in the frame.
A simple and compact design is achieved if the apparatus is disposed in a vacuum chamber, wherein the drive shafts for the lifting devices are fed through a wall of the vacuum chamber in a vacuum-tight manner so that the motors for driving the individual lifting devices are situated outside the vacuum chamber.
The motors are attached in a fixed manner on the vacuum chamber. So that it is possible to transmit torque to the lifting device in every position of the frame, every connection between a motor and the associated lifting device that transmits torque has a telescopically extendable section.
In the simplest case, the shafts are formed by cage bars arranged in a circle, which extend between an upper and lower rotary disk.
The lifting devices, which are configured as spindle drives, each have a laterally projecting extension, which engages in the associated shaft formed by cage bars.
In order to be able to switch between the shafts of a frame, a feed sleeve is disposed on the upper side of the frame for each crucible, through which a material bar can be inserted through the crucible base into the crucible. Each feed sleeve is equipped with a clamping device for holding the material bar in the feed sleeve.
The invention will be explained in more detail in the following on the basis of an exemplary embodiment.